In packaging of wire bonded dies, encapsulation is necessary to protect the integrated circuit die from mechanical stresses and chemical attack which may be encountered in the typical operating environment of the device. Single chip modules, for example, have an integrated circuit die adhesively bonded within a recessed cavity of a carrier substrate. The generally rectangular die includes a series of fine wire bonds that extend from a surface of the die and attach to wire bonding areas located on a surface of the carrier substrate. The wire bonds carry electrical signals between the integrated circuit die and individual contact pads located in the wire bonding areas of the carrier substrate. In the past, encapsulation of a wire bonded die and its carrier substrate, such as a conventional lead frame, was achieved by placing the die and carrier substrate in a mold, and then injecting encapsulant material into the mold through one or more injection gates. The encapsulating material filled the mold cavity to cover the wire bonded die and, after the encapsulant cured and hardened, the mold was removed to reveal a molded encapsulated part.
However, with the increased use in the electronics industry of area array packaging for wire bonded dies, such as ball grid array (BGA) interconnect packages, the increased size of advanced integrated circuit dies, the higher number and tighter spacing of the fine wire bonds, and the overall geometry of the ball grid arrays make molded encapsulation a less desirable process. For these reasons, liquid encapsulation of advanced wire bonded dies with two-part liquid epoxies and the like has become increasingly popular for high volume integrated circuit package applications.
With epoxy-based liquid encapsulation processes, the wire bonded die and carrier substrate are encapsulated with a viscous, self-leveling material that is dispensed from a moving dispensing needle or nozzle located above the part. The dispensing needle is programmed to follow a programmed dispensing path over the wire bonded die to dispense the liquid encapsulant over the part in a predefined pattern. Typically, the dispensing pattern is programmed as a single glob shot, shrinking square, shrinking oval or zigzag for dispensing the encapsulant relatively evenly over the wire bonded die, including the fine wire bonds and wire bonding areas. Each of these known dispensing patterns may further include a rectangular dispense pattern located outside of the initial pattern to further enhance the encapsulation process.
In any encapsulant dispensing process, several critical issues must be addressed, including the elimination of any voids or bubbles in the encapsulant material, the dispensing of the correct volume of encapsulant on the part in an accurate and repeatable manner, and the speed of the encapsulation process. Notwithstanding the advances that have been made in liquid encapsulation of wire bonded dies using area array interconnect packages, there is a need for an encapsulation process that substantially eliminates trapped voids or bubbles in the protective encapsulating layer of an advanced wire bonded die which may lead to premature part failure. There is also a need for an encapsulation process that relatively quickly and evenly dispenses liquid encapsulant in a predefined pattern to provide an overall level encapsulation of advanced wire bonded dies. Additionally, there is also a need for an encapsulation process that provides substantially uniform and repeatable encapsulation of wire bonded dies for high volume integrated circuit packaging applications. Moreover, there is a need for an encapsulation process that permits increased flowrates of encapsulating material to be used which results in a higher volume of parts through the encapsulation process.